Tensioning a wire fence properly is one of the most important steps in building a fence that will last for years without sagging, breaking, or letting stock through. Done right, a well-tensioned fence is safe, tidy, and effective — whether you're running sheep, cattle, or simply marking a boundary. Here's how to do it correctly.
Understanding the Basics of Wire Fence Tension
A wire fence works by holding tension between solid anchor points — typically strainer posts (also called end posts or corner posts) at each end or change of direction. The wires are pulled tight between these posts and held in place by staples or wire clips on the intermediate (line) posts in between.
The most common wire types used in New Zealand are:
- High-tensile wire (usually 2.5 mm) — strong, springy, and the standard choice for most rural fencing
- Mild steel wire — softer and easier to work with but less durable
- Barbed wire — used for stock control; handle with care
- Netting or mesh (e.g. ring-lock or hinge-joint) — requires tensioning across the full width
Always check the wire manufacturer's recommended tension rating before you start, as over-tensioning can snap wires or pull out strainer posts.
Tools You'll Need
- Wire strainer (hand ratchet or mechanical/chain strainer)
- Wire cutters (heavy-duty fencing pliers)
- Fencing pliers (multi-tool for stapling, cutting, and twisting)
- Staple gun or hammer and fencing staples
- Straining bar or gripple tool (if using gripple joiners)
- Gloves and eye protection — essential when working with tensioned wire
Step 1 — Set Your Strainer Posts Correctly
Before you tension anything, your strainer posts must be solid. These are typically 125–150 mm diameter posts, set at least 900 mm into the ground (deeper in soft or sandy soils), and braced with a diagonal strainer brace or box strainer assembly. A strainer post that moves under load will ruin your tension and can be dangerous.
If you're unsure whether your strainer assembly is adequate, consult a qualified fencer — you can find local fencing professionals on tradedirectory.co.nz.
Step 2 — Run Out Your Wire
Unroll the wire along the fence line, keeping it off the ground where possible to avoid kinks. Attach one end securely to the first strainer post using a figure-eight knot or a crimping sleeve, then run the wire to the far strainer post. Leave enough tail (at least 300–400 mm) at each end for tying off.
For netting, unroll it along the fence line and attach the leading edge to the first strainer post before running it out.
Step 3 — Attach the Wire Strainer
At the far strainer post, attach your wire strainer (ratchet or chain type) between the post and the wire. Many fencers use a straining bar looped through the wire to give the strainer something to grip. Alternatively, gripple joiners with a gripple tool are a popular modern method that makes tensioning faster and neater.
Step 4 — Apply Tension Gradually
Ratchet or crank the strainer slowly, applying tension gradually and evenly. For high-tensile wire, the general rule of thumb is to tension until the wire has a slight spring to it when plucked — it should "sing" rather than feel slack or drum-tight. Over-tensioning is a common mistake; it stresses the wire and the posts and can cause snapping, especially in cold weather when wire contracts.
As a rough guide for high-tensile wire, most manufacturers recommend a tension of around 800–1,000 Newtons for standard rural fencing, but always defer to the wire manufacturer's specifications.
Tensioning Netting or Mesh
For ring-lock or hinge-joint netting, attach a straining bar through the end of the netting and use two strainers (top and bottom) to pull the netting evenly. Tension the top wire first, then the bottom, then work through the intermediate wires to keep the mesh square.
Step 5 — Fasten to Line Posts
Once the correct tension is achieved, staple or clip the wire to each intermediate (line) post. Importantly, do not drive staples in fully on line posts — leave them slightly proud so the wire can move slightly with temperature changes. On strainer posts, staples or ties should be firm and secure.
For timber posts, use fencing staples at a slight angle to the grain for better holding power. For steel posts (waratahs), use the wire clips or ties supplied with the posts.
Step 6 — Tie Off and Finish
Once stapled, release the strainer and tie off the wire end at the strainer post using a figure-eight or wrap-and-twist method. Trim any excess wire and fold the tail back safely to avoid sharp ends. Check the full fence line for consistent tension and any missed staples.
Safety Notes
Tensioned wire stores a significant amount of energy. If a wire snaps or a strainer slips, it can cause serious injury. Always:
- Wear gloves and safety glasses
- Stand to the side of the wire, never directly behind the strainer
- Keep bystanders and children well clear
- Follow safe work practices as outlined by WorkSafe NZ
Do You Need a Building Consent?
Most rural and residential boundary fences in New Zealand do not require a building consent under Schedule 1 of the Building Act, but there are exceptions — for example, fences over 2.5 m high or retaining walls combined with fencing. Always check with your local council before starting, as rules can vary. MBIE Building Performance has useful guidance on what work is exempt.
When to Call a Professional
Wire fencing looks straightforward but getting the strainer post assembly, tension, and line post spacing right takes experience. Consider hiring a qualified fencer if:
- You're fencing a large area or steep terrain
- You're unsure about strainer post sizing or bracing
- You're working near roads, waterways, or boundaries where errors could have legal or safety consequences
- You need electric fencing installed (energiser wiring should be done carefully and to manufacturer specs)
A professional fencer will get the job done efficiently and to a standard that lasts. Find qualified local fencers on tradedirectory.co.nz.
